Lead-acid storage battery grids are made by a variety of casting techniques including (1) directly casting a lead alloy into a gridform such as by the processes disclosed in U.S. Pat. Nos. 3,789,910 or 4,415,016; or (2) casting a strip of the alloy (e.g., see Atkins et al. U.S. Pat. No. 4,122,890), rolling the strip into a thin ribbon and thereafter expanding the ribbon into grids such as by the process disclosed in Daniels et al U.S. Pat. No. 3,945,097. Such processes require that large batches of molten lead alloy be prepared to insure a ready supply of melt of the proper composition for dispensing to the casting machines during the course of a production run. This is done by providing a large (e.g., 25 ton) melting furnace which is full of melt and maintained at about the casting temperature to be used. As casting progresses, the melt in the furnace is replenished by periodically charging the furnace with appropriate quantities of the alloy's ingredients. Lead hogs, prealloyed by the lead supplier, may be used to charge the furnace but are not cost effective. Rather, it is more cost effective for the manufacturer of the castings (hereafter casters) himself to add separate hogs of lead and pigs of each of the other ingredients (e.g., tin, calcium, etc.) to the melt in the furnace as required to maintain an adequate supply of melt therein. The addition of solid hogs (i.e., 1920 lbs.) and of smaller pigs of the other ingredients tend to chill the melt and thereby create a demand for additional direct heat to be added to the furnace by the furnace's heaters in order to maintain the casting temperature. Moreover, such additions temporarily disrupt the homogeneity of the melt composition in the furnace until the hogs/pigs dissolve and mix with the rest of the melt.
The addition of even minor amounts (i.e., less than about 0.06% by weight) of alloyants such as Al, Cu or Ni which have a solid solubility in lead of less than 0.06% by weight under equilibrium conditions (hereafter low lead solubility), and a much higher melting point than lead cannot be added so simply and have heretofore required superheating of all the melt in the furnace to ensure dissolution of the alloyant. In this regard for example, at least one manufacturer of lead hogs prealloyed with about 0.02 weight % Al prepares a 73% Ca and 27% Al master alloy which melts at about 1100.degree. F., heats an entire batch of melt up to about 1100.degree. F., plunges the master alloy beneath the melt, agitates the melt and continues the process until all of the master alloy is dissolved and thoroughly mixed throughout. Thereafter the melt is cast into hogs which are then cooled back down to room temperature for shipment. Such practices waste heat and time, place an unnecessary thermal strain on the melting furnace and add to the cost to purchasers of the hogs. Were a casting manufacturer to add such alloyants in the same manner at the casting site, he would experience essentially the same disadvantages as the hog supplier.
Accordingly, it is an object of the present invention to provide a lead alloying system including process and apparatus for simply and economically alloying large batches of lead with a minor amount of a low-lead-solubility, high-melting alloyant in a minimum amount of time and with a minimum amount of additional heat so as not to delay the process, add to the heating expense or place an unnecessary thermal stress on the melting furnace. It is another object of the present invention to utilize such an alloying system as part of a complete casting operation. These and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.